Chemical and Physical Modification of Petroleum, Coal-tar, and Coal-extract
Pitches by Air-blowing
Nathan King
Treatment by air-blowing was pursued as a process to modify the properties of
pitches. The focus of this research was to compare the effects of air-blowing a coalextract
pitch with a petroleum pitch and coal-tar binder pitch. Hydrogenation of a
bituminous coal in tetralin was used to produce the coal-extract pitch. The three pitches
were air-blown in a 1-liter autoclave at temperatures of 250°C, 275°C, and 300°C for
various time periods. The air-blown pitches were then characterized by softening point,
coke yield, solubility, viscosity, density, elemental analysis, thermogravimetric analysis,
FTIR, and optical texture. The results showed that air-blowing was a very effective way
to increase the softening point, coke yield, density, and viscosity for all of the materials.
The viscosity of the pitches was described well using the WLF model. Air blowing
increased the carbon-to-hydrogen ratio, but little oxygen was incorporated into the pitch
product. van Krevelen diagrams indicated that the coal-extract, petroleum, and coal-tar
pitch each followed different mechanisms during the course of air blowing, emphasizing
that compositional details must be considered in describing reaction details. Kinetic
modeling of the air-blowing process showed an activation energy of approximately 16
kcal/mol for all three pitches. The optical texture of all of the pitches was purely
isotropic before and after air-blowing treatment. The pitches were carbonized and their
respective green cokes displayed a highly anisotropic structure.